app-MAIL-temp/app/db.py

import sqlalchemy
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session
from sqlalchemy.orm import sessionmaker

from app import config


engine = create_engine(
    config.DB_URI, connect_args={"application_name": config.DB_CONN_NAME}
)
connection = engine.connect()

Session = scoped_session(sessionmaker(bind=connection))

# Session is actually a proxy, more info on
# https://docs.sqlalchemy.org/en/14/orm/contextual.html?highlight=scoped_session#implicit-method-access
Session: sqlalchemy.orm.Session